JP2000278542A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform natural edge emphasis among colors which do not change so much in lightness or density by extracting chrominance information from color image information, detecting a chrominance edge from the color difference information, calculating the chrominance edge quantity at the chrominance edge and calculating a chrominance emphasis quantity on the basis of the quantity of the chrominance edge. SOLUTION: When color image data of multitone which are read by a scanner or are stored in a memory of a computer are inputted in an image processor 10, chrominance information is first extracted from a whole or a part of the color image data in a chrominance information extraction part 12. Subsequently, it is decided in a chrominance edge detection processing part 14 whether a part where a gradient of the chrominance information is large, that is, a part where a change in hue is large, exists in the extracted chrominance information or not and a quantity of chrominance edge emphasis is calculated on the basis of the chrominance edge. Then, in a chrominance correction part 16, an edge of an original color image is emphasized on the basis of the calculated quantity of the chrominance edge emphasis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus incorporated in, for example, a digital color copying machine for correcting and outputting color image information input from a predetermined image input device.

[0002]

2. Description of the Related Art Conventionally, for example, when color image information read by a document reading device or stored in a memory of a computer is output on a display screen, or a photosensitive member is exposed based on the color image information. When an image is to be formed on the photoreceptor, a portion where the gradient of the brightness data and / or the density data is high, that is, a portion where the brightness difference or the density difference between adjacent data is large, is emphasized for the color image information. It is known to perform lightness edge enhancement processing and / or density edge enhancement processing, and particularly to perform edge enhancement of achromatic components (for example, black and white components).

[0003]

In the conventionally known brightness edge enhancement and density edge enhancement processing, a remarkable effect can be obtained with respect to edge enhancement of achromatic component data.
For example, the effect of edge emphasis is less likely to appear between colors that change in hue but have little change in brightness or density, such as green and blue, and an image in which the boundary between the two colors is clear cannot be obtained. Therefore, when edge enhancement processing is performed on a color character on a color background such as a blue character on a green background, the character quality is lower than that of a character composed of achromatic component data such as black. There was a problem of becoming. Further, in the conventional brightness edge enhancement processing, when brightness edge enhancement is performed on a relatively dark portion of an image, the brightness of a color may change, and the image may become unnatural.

[0004] The present invention has been made in view of the above technical problems, and has as its object to provide an image processing apparatus capable of performing natural edge enhancement between colors having little change in brightness and density.

[0005]

According to the present invention, there is provided an image processing apparatus for processing and outputting color image information input from a predetermined image input device, wherein the color difference information for extracting color difference information from the color image information is provided. Extracting means for detecting a color difference edge from the color difference information extracted by the color difference information extracting means,
Color difference edge detection means for calculating the color difference edge amount of the color difference edges, color difference enhancement amount calculation means for calculating the color difference enhancement amount based on the color difference edge amount calculated by the color difference edge detection means, and color difference enhancement amount calculation means And a color difference emphasis correction means for emphasizing and correcting the color difference information using the color difference emphasis amount calculated by the above.

With this configuration, after detecting a high gradient portion, that is, a portion having a large change in hue (a so-called color difference edge) in color difference information extracted from color image information input from the outside, the color difference information is detected. The color difference emphasis amount is calculated from the portion, and each color difference data is corrected based on the calculated color difference emphasis amount, so that the color difference edge can be emphasized. As a result, a subtle change in color is emphasized, and the boundary between colors is clear. For example, the edge of a color character on a color base is also enhanced, thereby improving the character quality. Also, for a relatively dark part of the image, edge enhancement can be performed without changing the color brightness, and a natural image can be obtained.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a part of the configuration of the image processing apparatus according to the embodiment of the present invention. The image processing apparatus 10 is incorporated in, for example, a digital color copying machine or the like, and is connected to an image input apparatus 20 such as a document reading apparatus (a so-called scanner) or a computer.
Receives the digital color image information output from the digital color image information, performs a predetermined color difference edge enhancement process on the digital color image information, and outputs the digital color image information to the image output device 30.
The configuration includes a color difference information extraction processing unit 12, a color difference edge detection processing unit 14, and a color difference correction unit 16.

In the image processing apparatus 10 having such a configuration, when multi-gradation color image data read by a scanner or stored in a memory of a computer is input, first, the color difference information extraction processing section 12 The color difference information is extracted from the whole or a part of the color image data. Subsequently, the color difference edge detection processing unit 1
4, in the extracted color difference information, a portion where the gradient of the color difference information is high, that is, a portion where the change in hue is large (hereinafter, referred to as a portion).
It is determined whether or not there is a color difference edge), and if there is a color difference edge, based on the color difference edge,
A color difference enhancement amount is calculated. Then, the color difference correction unit 16
In, the edge of the original color image data is enhanced based on the calculated color difference enhancement amount.

FIG. 2 is a block diagram relating to data processing performed in the image processing apparatus 10. In the image processing apparatus 10, first, in an HVC conversion (color space conversion) processing unit 21, input RGB image data (FIG.
The entirety or a part thereof (RI, GI, BI) is converted into lightness data Y and color difference data Cr, Cb. HV
The brightness data Y and the chrominance data Cr and Cb after the C conversion are used as the brightness edge determination unit 22 and the chrominance edge determination unit 2, respectively.
4r, 24b.

The brightness edge determination section 22 calculates the brightness edge amount EY from the brightness data Y, as is known in the prior art.
Is calculated. The calculated brightness edge amount EY is sent to the brightness enhancement amount calculation unit 23, and the brightness enhancement amount BY is calculated based on the brightness edge amount EY. Note that the brightness enhancement amount calculation unit 23 obtains the brightness enhancement amount BY by performing conversion using a RAM for an LUT (look-up table).

On the other hand, the color difference edge detector 24
In r and 24b, edges in the color difference data Cr and Cb sent from the HVC conversion processing unit 21 are detected. In this case, when the existence of the chrominance edge is confirmed, the chrominance edge amounts DCr and DCb at each edge are calculated through an edge determination circuit using a primary differential filter composed of, for example, a 5 × 5 matrix.

Subsequently, the color difference edge detectors 24r, 2
The color difference edge amounts DCr and DCb calculated in 4b are
The color difference edge determination unit 25 sends the color difference edge amount D
The total color difference edge amount EC (= DCr +
DCb) is required. In this embodiment, the larger one of the color difference edge amounts DCr and DCb is used as the total color difference edge amount E.
C. The sum of the color difference edge amounts DCr and DCb may be used as the total color difference edge amount EC without being limited to this. Further, in the color difference emphasis amount calculation unit 26,
The color difference enhancement amounts BCr and BCb are calculated from the total color difference edge amounts EC obtained by the edge determination unit 25. In this embodiment, as in the case of the brightness enhancement amount calculating section 23, the conversion is performed by the LUT RAM and the calculation is performed.

In the color difference correction section 27, the calculated color difference emphasis amounts BCr, BCb (= Q) and the color difference data Cr, Cb (= P) after the HVC conversion are added. As a result, the color difference data Cro and Cbo (=
P + Q) is obtained. On the other hand, the brightness enhancement amount BY (=
Q) and the above-described brightness data Y (= P) after the HVC conversion are added to obtain brightness data YO (= P + Q) with brightness edge enhancement. Finally, the brightness data YO and the color difference data Cro and Cbo obtained by performing the edge enhancement processing as described above are converted into color image data RO, GO and BO in the inverse HVC conversion processing unit 28, and the image output device 30 Output to

In this embodiment, in order to correct the color difference data Cr and Cb input from the image input device to emphasize the edges, the color difference enhancement amounts BCr and BCb calculated by the color difference enhancement amount calculation unit 34 are used. The color difference data Cr and Cb are added to the color difference data. However, the present invention is not limited to this. For example, the color difference correction unit calculates the color difference enhancement amounts BCr and BCb (= Q) calculated by the color difference enhancement amount calculation unit 34. HVC
The converted color difference data Cr and Cb (= P) may be multiplied. In another embodiment, the color difference enhancement amount calculation unit 34 multiplies BCr and BCb by two coefficients b and c,
Four color difference enhancement amounts BCrb, BCbb (= Q), BCr
After calculating c, BCbc (= R), the color difference correction unit adds BCrc, BCbc to the color difference data Cr, Cb after the HVC conversion.
The color difference data Cro and Cbo (P × R + Q) may be obtained by multiplying BCbc and further adding BCrb and BCbb.

As described above, in the image processing apparatus according to the present invention, a color difference edge is detected from color difference information extracted from digital color image information input from the outside, and a color difference enhancement amount is calculated from the color difference edge. The color difference edges can be enhanced by correcting the respective color difference data based on the obtained color difference enhancement amount. As a result, subtle color changes are emphasized and the boundaries between colors are clear, so for example, the edges of color characters on the color base are also emphasized,
The character quality is improved. In addition, a natural image can be obtained by performing edge enhancement on a relatively dark portion of an image without changing color brightness.

FIG. 3 is a flowchart of the color difference edge enhancement process. First, in step # 21,
The RGB data obtained from the image input device is converted into brightness data Y and color difference data Cr and Cb by HVC conversion processing. Subsequently, it is determined whether or not a color difference edge exists for the color difference data Cr (# 22). If it is determined that a color difference edge exists, in step # 23,
The color difference edge amount DCr for the color difference data Cr is calculated, and thereafter, the process proceeds to step # 25. On the other hand, if it is determined that there is no chrominance edge, the chrominance edge amount DCr is set to 0 in step # 24.
Proceed to.

Following the color difference data Cr, the color difference data Cb
Is determined as to whether or not a color difference edge exists (♯
25). If it is determined that a color difference edge exists,
In step # 26, the color difference edge amount DCb for the color difference data Cb is calculated, and thereafter, the process proceeds to step # 28. On the other hand, if it is determined that there is no color difference edge, the color difference edge amount DCb is set to 0 in step # 27, and then the process proceeds to step # 28. In step # 28, the total color difference edge amount EC is calculated from the calculated color difference edge amounts DCr and DCb. Next, the edge enhancement amounts BCr and BCb are calculated from the calculated total color difference edge amounts EC (# 2
9).

In step # 30, the brightness data Y
, It is determined whether or not there is a lightness edge. If it is determined that a lightness edge exists, step ♯
At 31, the amount of emphasis BY for the brightness data Y is calculated, and thereafter, the process proceeds to step # 33. On the other hand, if it is determined that there is no lightness edge, step ♯
After setting the emphasis amount BY at 32 in step 32,
Go to 33. Subsequently, in step # 33, an enhancement process is performed on the brightness data Y and the color difference data Cr and Cb based on the calculated enhancement amounts BY, BCr and BCb. And
In step # 34, the brightness data YO and the color difference data Cro, Cbo that have undergone the edge emphasis processing are reconverted into RGB data by the inverse HVC conversion processing.

As described above, the image processing apparatus 1 according to the present invention
In the case of 0, the input pixel data is subjected to the edge enhancement processing for the brightness information, and the edge enhancement processing is also performed to the color difference information. Therefore, for example, although the hue changes like green and blue, the brightness is changed. Even between colors with little change in density and density, an image in which the boundary between the two colors is clear can be obtained.

The present invention is not limited to the illustrated embodiment, and it goes without saying that various improvements and design changes can be made without departing from the spirit of the present invention.

[0021]

As is apparent from the above description, according to the present invention, a color difference edge is detected from color image information input from the outside, and the amount of the color difference edge in the color difference edge is calculated. By correcting the data,
Processing that emphasizes the color difference edge can be added. As a result, a subtle change in color is emphasized, and the boundary between colors is clear. For example, the edge of a color character on a color base is also enhanced, thereby improving the character quality. In addition, a natural image can be obtained by performing edge enhancement on a relatively dark portion of an image without changing color brightness.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram relating to data processing in the image processing apparatus.

FIG. 3 is a flowchart illustrating edge enhancement in the image processing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image processing apparatus 12 ... Color difference information extraction processing part 14 ... Color difference edge detection processing part 16 ... Color difference correction part 20 ... Image input device 30 ... Image output device

Continued on the front page F term (reference) 5C066 AA03 AA11 BA20 CA09 EA11 EC02 EE03 EF03 GA01 GA02 GA05 GB01 HA02 JA01 KA08 KD06 KE02 KE03 KE04 KE16 KL01 LA02 5C077 LL19 MP08 PP09 PP31 PP32 PP35 PP37 PP47 PP68 PQ06 H11 LA15 LB00 MA05 NA06 PA02

Claims (1)

[Claims] 1. An image processing apparatus for processing and outputting color image information input from a predetermined image input device, comprising: color difference information extracting means for extracting color difference information from the color image information; A color difference edge detecting means for detecting a color difference edge from the color difference information extracted by the means, and calculating a color difference edge amount of the color difference edge; and calculating a color difference enhancement amount based on the color difference edge amount calculated by the color difference edge detecting means. An image processing apparatus comprising: a color difference enhancement amount calculating unit that performs color difference enhancement; and a color difference enhancement correction unit that enhances and corrects the color difference information using the color difference enhancement amount calculated by the color difference enhancement amount calculation unit.